This invention relates to manufacture of papermaking fabrics and particularly to wet felts and occasionally dryer fabrics.
Over the years, papermakers have used developments in wet felt design to improve water removal in the presses of papermaking machinery. With the advent of monofilament and multifilament yarns in the 1960's, "batt-on-base" and "batt-on-mesh" designs were introduced. In these designs, carded batts are needled into woven base fabrics.
Conventionally, several layers of batt are cross-lapped onto the base fabric in the cross-machine direction. For example, see U.S. Pat. No. 3,257,259. When the batts are cross-lapped upon the base fabric for needling, the fibers are generally oriented in the cross machine direction rather than the machine direction. In the case of wet felts, water must be pressed from the felt for water removal from the paper fiber matt. Cross-machine oriented fibers are thought to restrict the lateral movement of the water and adversely affect water removal from the sheet.
Related U.S. Pat. Nos. 3,879,820 and 3,920,511 disclose a papermaker's felt and method in which the fibers are oriented substantially longitudinally to make a substrate by using numerous transfers of the batt upon aprons, reorientations along tortuous paths, and other batt manipulations in a rather complicated manner. A batt is then needled to the substrate crosswise to the felt travel.
U.S. Pat. Nos. 4,553,289; 1,953,457; and 3,713,933 relate generally to the art of building up fibrous batts either in juxtaposed or superposed relation. In the first two patents, general batts are reoriented 90 degrees by using angularly disposed guide rods so that the resulting batt is aligned lengthwise with a conveyer. These patents are related only generally and not directly to the present invention.
U.S. Pat. No. 4,878,278 relates generally to the act of applying fiber batts to the base fabric in the machine direction of the papermaking fabric. As the fibers forming the batt extend in the length direction of the batt, they are arranged to extend in the machine direction of the papermaking felt. A major drawback to this method is that jointing must occur sequentially as each batt must be attached to the base fabric as it is positioned thereon. Also, starting and ending lines appear lengthwise the felt across the width thereof. Any over or under lapping of these lengthwise splice lines may cause lengthwise marking of the paper.
In view of the above disadvantages, it is an object of the invention to apply the batts cross-machine-wise while using batts having machine direction oriented fibers on the felts. The benefits of such batts can be twofold: (1) by eliminating the butt joint in the batt, the tendency of lengthwise sheet marking is greatly reduced; and (2) the surface of such felts is exceptionally smooth and lacks needle marks. This not only enhances the water removal due to more uniform pressure application from the press rolls to the sheet, but also improves the surface quality of the sheet for the lack of needle marks.
Another object of the invention is to provide a method and apparatus for making a papermakers felt which includes a fiber batt needled into a base fabric in which the fibers in the fiber batt extend generally in the machine direction which facilitates water removal as well as to improves the sheet quality.
Another object of the invention is to provide a wet felt having machine direction oriented fibers which are laid upon a base fabric and needled without excessive fiber manipulation.
Still another object of the invention is to provide a wet felt in which the fiber batts extend transversely across the entire width of the base fabric while at the same time having the fibers forming the batts extending in the length direction of the base fabric so that full width needling of the batt to the base fabric is facilitated.
Still another object of the invention is to produce a felt with an under layer of the batt fibers oriented in cross-machine direction and the top layers of the batt fibers oriented in the machine direction so as to create a "shingle" effect of the batt fibers. Such structure is believed to have better compaction resistance.